Piston and method of making the same



Oct. 22, 1929. z. JEFFRIES ET AL 1,732,557

PISTON AND METHOD OF MAKING THE Sm Filed April 21, 1924 m mm ,0 A 9 l I/ Z 7 /0 A TTORNEYS.

Patented Oct. 22, 19 29 UNITED STATES PATENT OFFICE ZA'Y JEFFRIES" AND ROBERT S. ARCHER, 0F CLEVELAND, OHIO, ASSIGNORS TO ALU- MINUM COMPANY OF AMERICA, 0]? PITTSBURGH, PENNSYLVANIA, A CORPORATION i0]? PENNSYLVANIA PISTON AND METHOD OI MAKING THE SAME Application filed April 21,

Our invention relates to aluminum alloy pistons for internal combustion engines and more particularly to such pistons which have been heat treated and which may also have one or more flexible skirt portions. It also relates to a new and improved method of making such pistons.

It has as an object the provision of an aluminum alloy piston characterized as being capable of resistingwear in the bosses, ring grooves and bearing portions of the skirt to an extent considerably in excess of that heretofore obtained.

Another object is the provision of an aluminum alloy piston having a flexible skirt portion and characterized as being of increased hardness, resistance to permanent deformation and fatigue, and elevated elastic limit, all as compared with aluminum'alloy pistons made prior to our invention.

Another object is to devise a new and improved method of producing a piston having the foregoing properties and characteristics.

Aluminum alloyv pistons have heretofore frequently proven somewhat unsatisfactory, because of a tendency to wear in the ring grooves, wrist pin bosses and on the thrust faces of the skirt or at any of these points. By our invention, we have been able to pro duce an aluminum alloy piston with considerabl increased resistance to wear at any or all 0 such points, such a piston being thereby rendered satisfactory, for use with ferrous metal rings, wrist pins and cylinders for a length of time favorably comparable to the length of life of the ordinary cast iron piston.

It has also been found that pistons which have one or more flexible portions in the skirt, as are formed by slits in the skirt, often become less fit for service after a short period of use, due in part to failure of the flexible portion or portions to function properly throughout the full life of the piston. This characteristic is, however, not confined to aluminum alloy pistons but is present in pistons composed of other material, such for example as cast iron. In the o eration of a piston having one or more exible portions in its skirt, it seems probable that the 1924. Serial No. 707,868.

flexible portions are flexed repeatedly during the operation of the piston, so that the elastic limit of the metal maybe exceeded and the metal therein stressed, so that the flexible portion or portions take a permanent set, after which such portions may no longer come into contact with the walls of the engine cylinder. The bearing surface of the piston is thus diminshed and the function of the flexible portion largely, if not entirely, lost, both of which facts tend to render the piston less suitable for further service.

lVe have discovered, however, that satisfactory aluminum alloy pistons can be constructed by selecting suitable metals or alloy compositions and subjecting such metals, in the form of a piston casting, to suitable heat treatment capable of developing the physical properties such as increased hardness, elevated elastic limit and tensile strength' such a piston when so treated and provided with a flexible portion or portions in the skirt, as may be done by forming intersecting slits therein, has been found to retain its original resiliency in the flexible portions throughout substantially the entire life of the piston and the flexible portions have not collapsed, that is, taken a permanent set in a position substantially out ofcontact with the cylinder walls and have not broken as readily as heretofore.

For convenience and brevity we have. elected to describe, in the following specification, our invention with particular reference to a specific form of piston shown by the accompanying drawings and with a particular alloy composition, namely: an aluminum copper alloy suitable for piston requirements. It is to be understood, however, that by so doing, we do not limit our invention to the particular modifications described, but that on the contrary the scope of our invention is to be determined by what is claimed.

In the drawings:

Figures 1 and 2 represent side elevational views at right angles to each other of one in Figures 1 and 2 looking into the open end I thereof. Y

' is operating in an engine and is provided- Figure 4 is-a cross sectional view taken on line Ir-40f Figure 3.

The piston shown in the drawing comprises a head 1, skirt 2, bosses 3 attached to the head by a web 4 which is also connected to the bearing portions 5 of the skirt. Between the head and the upper end of the skirt 2, cuts or slits 6 are formed through the wall of the piston to separate the bearing walls 5 of the piston from the adjacent portions of the head. In the modification shown, the webs 4am offset inwardly with respect to the outer circumference of the skirt 2 from their point of attachment to the head to a point below the bosses 3 and are there disconnected from the adjacent portions of the skirt 2 by spaces or slits 7. By referring to Figure 3 it will be observed that the webs 4 at one side of the .bosses are curved circumferentially of the piston and sweep outwardly as at 8, merging into theadjacent bearing wall 5. This hearing face 5 is the face which takes the lesser thrust of the connecting rod when the piston with a longitudinal slit 9 intersecting at its upper end the circumferentially extending slit 6 and extending toward or to the open end of the skirt. The curved portions 8 of the webs 4 cooperate with the slit 9 to form flexible portions of the skirt which tend to yield under the side thrust of the piston when it is operating, such yielding or bending causing each flexible portion to bend inwardly toward the center of the piston when the thrust is applied and to return to-its normal position when the pressure is relieved.

Pistons somewhat similar to that herein illustrated have frequently become less suitable for service because the flexible portions corresponding to portions 10 in Figures 3 and 4 tend to break where connected to the remainder of the skirt or to take a permanent set when pressed inwardly toward the center of the piston. When breakage occurs the piston is, of course, of no further value and when apermanent set of the flexible portions occurs, with the portions bent in, that is, closer to the center of the piston than in the position here shown, the operation of the piston is considerably impairedand the piston may even be rendered useless.

We have found, however, that a piston of the type described when composed of an aluminum alloy containing from about 9.25% to about 10.25% copper, fr m about .9% to about 1.5% iron and from about 15% to about .35% magnesium, and the casting has been subjected to suitable heat treatment and thenprovided with intersecting slits to form flexible portions in the skirt, the flexible portions will resist breakage or permanent def-'- ormation for approximately the full life of the piston and, furthermore, that the hardness of the piston will be considerably 'increased with resulting slight wear and increased resistance to permanent deformation and fatigue in the flexible portions which tendsto produce a durable piston tightly fitting the cylinder for a long time.

Although certain limits of composition for the preferred aluminum alloy have been mencastingand fourth, machining the casting and providing it with a flexible portion in the skirt as by forming intersecting slits therein.

Any suitable method of combining the ingredients above set forth in the specified amounts to form a molten alloy suitable for casting may be employed. After the alloy has been prepared, it is cast-in a suitable mold. The resulting piston casting is heated usually for live hours or more at a temperature slightly below the freezing point of the eutectic in the alloy say at a temperature of about 510 C. and after being cooled quickly, that is, quenched, to room temperature is again heated, that is artificially aged, at a temperature of about 150 centigrade for sometimes as long as 50 hours or until the hardness has reached the desired or a maximum amount.

Pistons of the above mentioned composition which have been subjected to the foregoing heat treatment will be found to have a hardness ranging from about 125 to 155 Brinell as compared with about to 110 Brinell in the same alloy unheat-treated, an increased elastic limit, will be better adapted to resist Wear and will also be better adapted to resist permanent deformation as compared with unheat-treated castings of the same composition; a

We have found this combination of composition and heat treatment to be particularly useful and desirable in pistons of various types irrespective of whether the piston is slit or not. When pistons are cast of the metal specified and heat-treated as above set forth, the increased hardness of the piston resulting from heat treatment is also bencfi'cial becauseit reduces the wear of the piston on the cylinder and brings the piston more nearly to the same hardness as the cylinder wall, thereby tending to lengthen the life of each of these parts.

Where extreme hardness, for example, 155 Brinell is desired, we may often attain a hardness in a piston casting as high as about 160 Brinell by increasing the copper content of the alloy up to about 14% to 16% and correspondingly increasing the magnesium content to within the limits of about .35% and.

65%. This hardness can be obtained without substantial sacrifices of any of the desirable physical properties of a piston casting having the lower copper and magnesium content, except toughness.

* Having thus described our invention, what We desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. A cast piston composed of an aluminum base alloy containing between about 6% and 16% of copper and having a structure characteristic of such composition which has been heat treated by being quenched, and artificially aged.

2. A cast piston composed of an aluminum base alloy containing between about 9.25% and about 16% of copper and having a structure characteristic of such composition which has been heat treated by being quenched and artificially aged.

3. A cast piston composed ofan aluminum base alloy containing between 6% and about 10.25% of copper and having a structure characteristic of such composition which has been heat treated by being quenched and artificially aged.

4. A cast piston composed of an aluminum base alloy containing between about 9.25% and about 10.25% of copper and having a structure characteristic of such composition which has been heat treated by being quenched and artificially aged.

5. A piston as defined by claim-1 containing between about .15% and about 1.5% of. magnesium.

6. A piston as defined by claim 1 containing between about .15% and about 35% of magnesium.

i. A piston as defined by claim 2 containing between about .15% and about 1.5% oi magnesium.

8. A' piston as defined by claim 4 containing between about .15% and about 1.5% of magnesium.

9. A piston as defined by claim 4 containing between about .15% and about 35% of magnesium.

10. A piston as defined by claim 1 containing iron in substantial amounts but less than about 1.5%.

11. A cast piston composed of an aluminum base alloy containing between about 6% and about 16% of copper, between about .15% and about 1.5% of magnesium and iron in substantial amounts but less than about 1.5% and having a structure characteristic of such aged 13: A cast piston as define-d in claim 1 in which the casting also possesses a structure characteristic of such composition which has been chilled during the casting operation.

14.. A cast piston as defined in claim 12 in which the casting also possesses a structure characteristic of such composition which has been chilled during the casting operation.

15. The methodof heat treating a piston casting composed of an aluminum base alloy containing between about 6% and about 16% of copper which comprises the steps of heating the cast piston at a temperature slightly below the freezing point of the eutectic,

quenching the casting, and artificially aging,

the casting by reheating at a temperature of about 150 C. until the casting has attained a Brinell hardness number in excess of about 120.

16. The method of heat treating as defined in claim 15 in which the piston casting is composed of an aluminum base alloy containing between about 6% and about 16% of copper and between about .15% and about 1.5% of magnesium.

17. The method of heat treating as defined in claim 15 in which the piston casting is composed of an aluminum base alloy containing between about 6% and 16% of copper, and iron in substantial amounts but less than about 1.5%.

18. The method of heat treating as defined in claim 15 in which the piston casting is composed of an'aluminum base alloy containing between about 6%" andabout 16% of copper, between about .15% and about 1.5% of magnesium and iron in substantial amounts but less than about 1.5%.

19. The method of heat treating as defined in claim 15 in which the piston casting is composed of an aluminum base alloy containing between about 9.25% and about 10.25% of copper, between about 15% and about 35% of magnesium and iron in substantial amounts but less than about 1.5%.

20. The method as defined in claim 15 in which the casting is heated at a temperature slightly below the freezing point of the eutectic for about five hours.

21. The method as defined in claim 15 in which the casting to be heat treated is a chilled casting.

" 22. The method of heat treating a chilled piston casting composed of an aluminum containing between about 9.25 perbase allay cent an about 10.25 percent of copper, be-

tween about '.15 percent and about .35 percent of magnesium and iron in substantial amounts of less than about 1.5 percent which comprises the steps of heating the piston casting at a temperature slightly below the freezing point of the eutectic, quenching the casting, and artificially aging the casting by reheating at a temperature of about 150 degrees centigrade until the casting has attained a Brinell hardness number in excess of about 120. 7

In testimony whereof we hereunto afiix our signatures this 9th day of April, 1924.

- ZAY J EFFRIES.

ROBERT S. ARCHER. 

